It is known that coatings of the Aluzinc, aluminized or other type of the same genre having just been applied on a continuously moving metal strip must be solidified quickly to avoid intermetallic growth and obtain a correct microstructure in order to obtain a good corrosion resistance.
To solidify these coatings, pre-cooling units called “pre-coolers” or cooling units called “air cooling boxes or air coolers or ducts” are used, made using technologies and constructions of slots, nozzles or holes.
To simplify matters, reference will be made only to “coolers” hereafter. A series of coolers is typically installed above equipment for applying the coating up to the first return roller of the cooling tower.
The first cooling device(s) is (are) usually movable so as to provide the space necessary in order to maintain that equipment for applying the coating. These first cooler(s) generally use slot technology.
Each cooler is generally equipped with a fan operating with a variable speed motor, so as to be able to adjust its flow rate and cooling air pressure based on the strips and coatings to be treated.
If the impact of the cooling gas is too great when the coating has not yet set, a wavy layer or marks or lines may form, and the obtained final product may thus not comply with market quality requirements. The sensitivity of the liquid layer to these flaws essentially depends on the viscosity and the thickness of the liquid layer as well as the impact of the gas.
In the context of modifying the galvanization line and increasing production capacity, and therefore cooling, given that the heights of the towers are difficult to alter, a same poor quality phenomenon may be observed due to excessively intense cooling on a coating that has not yet solidified and usually in a certain temperature range.
Document US 2010/0200126 discloses equipment for producing, by hot dipping, galvanized/annealed steel sheets under optimal production conditions at any time despite rapid changes in the type of steel, coating and other outside factors. The unit for producing galvanized/annealed steel sheets by hot dipping is provided with a maintaining/cooling furnace for treating steel sheets having left a rapid heating furnace. Furthermore, the maintaining/cooling furnace is configured to allow a change of the ratio in the furnace of the maintaining zone to dip the steel sheet using dipping means at a maintaining temperature of 500 to 650° C. and of the cooling zone to cool the steel sheet using spray nozzles at an average cooling speed of 5° C./second or more.
Document US 2001/0000377 discloses a method and system for cooling a steel strip. A high water volume mist cooler and a low water volume mist cooler are positioned successively along the direction in which the steel strip moves. The high water volume mist cooler vaporizes a high water volume mist on the surface of the steel strip to cool the latter, and then the low water volume mist cooler vaporizes a low water volume mist on the surface of the steel strip to cool the later, thus cooling the steel strip while eliminating the influence of the transitional boiling, in order to prevent the steel strip from having a non-uniform temperature portion.
Document US 2011/0018178 discloses a method for acting on the temperature of a moving strip by blowing a gas or a water/gas mixture, in which a plurality of gas or water/gas mixture jets, extending toward the surface of the strip and arranged such that the impacts of the gas or water/gas mixture jets on each surface of the strip are distributed at the nodes of a two-dimensional network, are sprayed on each face of the strip. The impacts of the jets on one face are not across from the impacts of the jets on the other face, and the jets of gas or water/gas mixture come from tubular nozzles that are supplied by at least one distribution chamber and extend at a certain distance from the distribution chamber so as to leave a space free for the return flow of the gas or the water/gas mixture that is parallel to the longitudinal direction of the strip and perpendicular to the longitudinal direction of the strip.
Document US 2011/0030820 discloses a device for blowing gas on the face of a material in a moving strip, including at least one hollow box whereof one wall, turned toward the relevant face of the strip material, is equipped with a plurality of blowing orifices, making it possible to direct gas towards the face of the strip material. The hollow box is further laterally equipped, at least on one side thereof in reference to a median plane perpendicular to the plane of the strip, with a movable closing member serving to selectively close off some of the blowing orifices in order to adapt the width of the blowing zone to the width of the strip material in question.